Here’s a weird one… has anyone noticed something like this before? I’m trying to track down filament jamming issues, and not throw this Printrbot in the street in the process, and noticed these ridges in the extruded filament. Its like the teeth in the hobbed bolt are leaving marks in the filament that isnt being smoothed out in the extrusion process, except its sometimes intermittent and the pressure is about as backed off as it can be on the idler wheel. Thoughts?
What temperature are you extruding at? I assume you’re running PLA?
It’s certainly not your hob leaving marks. The plastic is fully molten before it goes through the nozzle. I used to have this and eventually decided some trickery of my nozzle just made the stream oscillate back and forth as it extruded into air. I think it’s just some particular pressure/temp combo does it.
Anyway, it shouldn’t cause any issues printing if that’s all it is. The plastic doesn’t have room to curl anywhere while printing. To test that it’s not causing any trouble, take the skirt from one of your prints and look at it under magnification (I used a cheap microscope for kids). If the lines of extrusion are smooth I wouldn’t worry about it.
Yeah, PLA… thats the next thing… this is a new Printrbot hotend which uses a ceramic heater instead of the terrible cartridge based hotend that came with it. But the new hotend reports temps that are almost exactly 20 degrees C cooler than they should be. I hooked up a 1% EPCOS to the hotbed sensor taped to the nozzle to verify. So this is actually set to 205C to compensate.
iv seen this when trying to extrude abs at low temp.
It’s caused by irregularity in the nozzle (slightly off-center drill, a burr or bit of burnt plastic on the end, tip dented or scratched, etc) causing the filament to curl into a tight helix as it leaves the nozzle. When it’s more extreme, it can cause the filament to curl up and stick to the nozzle. Unless it gets that bad, it shouldn’t be an issue. Extruding slower and/or at a higher temperature will also reduce the effect, because the polymer chains will have more time to realign going through the nozzle. For this reason, reducing this effect with heat/extrusion speed should correlate to less warp.
@Whosa_whatsis That makes sense and is typical. Odd that it does it intermittently but then you are dealing with many factors there. Here’s the latest fail: http://www.bwevans.net/files/epicfail.jpg Maybe 2 hrs into a 4 hr print. Did I mention brand new hotend?!
A classic example of a little piece of something stuck in the head of the extruder… You can turn up the heat and fix it for a short while, but if you want to fix it for good, then drill the small hole up again from the inside… It worked for me, and i had the exact same problem…
I have a hard time with that one… this is a new hotend and it happened on its first real print. I’ve written it up in full blog style here: http://hardwired.cc/?p=410 Comments appreciated and baseball bats after that.
So what’s everyone’s opinion of the Hyena hobbed bolt? I think that saved the day. Updates here: http://hardwired.cc/?p=410
from a physics perspective this is normal in a long drop laminar flow (sorry big words). it is caused by the back pleasure from the molten plastic hitting the print bed in the long fall. this slows down parts of the falling plastic but not uniformly, causes “piles” in the fluid flow. if you have a jar of honey with a honey wand you will see the same thing happen if you get the honey to the perfect height.
you can tell it is not the hobbled bolt because the top is not hobbled, but the bottom is.
@Camerin_hahn It does this even when it’s free-hanging, not just when the bottom touches the platform.
It should have some back pressure as it cools, but it would look slightly different. I really think this would be caused if the material was slightly too hot, but I will admit that I have no practical experience with setting print temps. I have only used commercial printers in the past.
@Camerin_hahn I’m pretty sure it’s all the way up, and that’s just a trick of the camera that makes it look like it starts part way down.
this is a question that may only be because of my ignorance, but does this the pattern change based upon the extrusion speed(I understand this has to be balanced with print temp)
@Nick_Parker grab the picture than zoom in, you can see it slowly develop along the fall length, That is why I was proposing that it a flowing fluid issue. it would be difficult for me to prove such a thing, as the filament is hardening as it falls, and it is not liquid at room temp. I will see if I can find something comparable in to express what I am saying